1. Field of the Invention
The present invention relates to a flare measuring mask and a flare measuring method of a semiconductor aligner.
2. Description of the Related Art
A semiconductor device is manufactured by repeating an exposure process of copying a circuit pattern formed on a mask as a mask pattern, on a semiconductor substrate by using an aligner. When there is an aberration on a lens for use in copying, there is a fear of deforming the circuit pattern while repeating the exposure process. Then, in the exposure process, a lens aberration of the aligner is measured so as to accurately form the pattern to be copied (for example, refer to Patent Article 1 or Patent Article 2).
In order to measure the lens aberration, various measurements are performed depending on the characteristic component of the lens aberration. A factor of causing the lens aberration is the flare component. Flare is a light which overlaps the original optical image and expands therefrom, reflected or diffused on a lens surface or a mask surface and flowing into the pattern to form. There is a lot of flare in a bright portion having a rough mask pattern and a little in a dark portion having a fine mask pattern.
Then, a shielding portion is provided around a measuring portion and flare is measured by varying a distance between the measuring portion and the shielding portion.
With reference to FIG. 11, the conventional flare measuring method will be described. FIGS. 11A and 11B are views for use in describing a flare measuring mask for use in the conventional flare measurement. FIG. 11A shows an example of a first measurement mask pattern as the measurement mask pattern of the flare measuring mask. The first measurement mask pattern 81 includes a first rectangular transparent area 87 formed by a first shielding area 89 and a first measuring portion 83 similar to the first transparent area 87 and inside of the first transparent area 87. The first measuring portion 83 includes a plurality of first stripe-shaped shielding portions 85 of the same figure aligned in parallel at regular intervals.
FIG. 11B shows an example of a second measurement mask pattern 91 that is the measurement mask pattern of the flare measuring mask. The second measurement mask pattern 91 includes a second rectangular transparent area 97 formed by a second shielding area 99 and a second measuring portion 93 similar to the second transparent area 97 and inside of the second transparent area 97.
The second measuring portion 93 includes a plurality of second stripe-shaped shielding portions 95 of the same figure aligned in parallel at regular intervals. The second measuring portion 93 has the same figure and the same size as the first measuring portion 83. Namely, the second stripe-shaped shielding portion 95 has the same line width, the same intervals, and the same number of lines as the first stripe-shaped shielding portion 85.
The first shielding area 89 is different from the second shielding area 99 in size and the first transparent area 87 formed by the first shielding area 89 is also different from the second transparent area 97 formed by the second shielding area 99 in size. Since the first measuring portion 83 and the second measuring portion 93 has the same figure and the same size, the width of an opening P1 of the first transparent area 87, namely a distance between the first measuring portion 83 and the first shielding area 89 is different from the width of an opening P2 of the second transparent area 97, namely a distance between the second measuring portion 93 and the second shielding area 99.
The first measurement mask pattern 81 is used to do patterning on a wafer through exposure of the photoresist provided on the wafer, hence to get a resist pattern. When the exposure is affected by the flare, the reflected and diffused light is irradiated on the photoresist. Therefore, the stripe-shaped pattern formed as the resist pattern becomes narrower in width and shorter in length than the pattern in the case of having no flare.
Consequently, with the same aligner, the second measurement mask pattern 91 having the opening width different from that of the first measurement mask pattern 81 is used to do the above-mentioned process of exposure and patterning. According as the opening portion becomes larger, it is much more, affected by the flare, exposure is performed and the line width of a resist pattern is measured with the flare measurement mask patterns of different opening widths P1 and P2, hence to obtain the influence of the flare (for example, refer to Patent Article 3).
There is also a flare measuring method with double exposure. FIG. 12 shows a measurement mask pattern 101 for double exposure, for use in the flare measurement through double exposure. This mask pattern 101 has a first measuring portion 103 including first stripe-shaped shielding portions 105 and a first transparent area 107. The measurement mask pattern 101 for double exposure is different from the above-mentioned first measurement mask pattern 81 and second measurement mask pattern 91 in that the pattern 101 doesn't have the first and the second shielding areas. The measuring portion 103 of the measurement mask pattern 101 for double exposure has the same structure as the first measuring portion 83 and the second measuring portion 93.
At first, two measurement mask patterns 101 for double exposure are prepared, and exposure is performed with these two measurement mask patterns 101 for double exposure. Next, a shielding pattern capable of covering the measurement mask pattern 101 for double exposure covers the measurement mask pattern 101 for double exposure, and then exposure is performed there. The exposures with the shielding patterns of different size (109a and 109b in FIG. 13) substantially have the same results as the exposures with the patterns of different opening widths P1 and P2 described with reference to FIG. 11, hence to obtain the influence of the flare. Here, FIGS. 13A and 13B are views for use in describing the double exposure shielding patterns.
[Patent Article 1] JP-A-2001-222097 (claims 1 to 3)
[Patent Article 2] JP-A-2001-296646 (claim 1)
[Patent Article 3] JP-A-2003-100624 (paragraph 49 to 50, FIG. 7)
The above conventional flare measuring method, however, has such a problem that the sensitivity is dull and the influence of the flare is difficult to measure in this case of measuring the influence thereof according to a change in the width of a line forming a stripe-shaped mask pattern. The width of the line in the measurement mask pattern is several dozen to several hundred nm and in order to measure the width of the line, it is necessary to use a critical dimension-scanning electron microscope (CD-SEM).
For example, in order to measure the influence of the flare in the orthogonal two directions, it is necessary to do the exposure process in another process.
In consideration of the above problems, an object of the invention is to provide a flare measuring mask and a flare measuring method capable of measuring the flare with an optical measuring instrument at higher sensibility.